There are numerous devices in the prior art whose primary function is to enable means for inflating an air bag within a vehicle for restraint of the occupants in the event of a collision. Those devices which have been proposed for vehicles of the automotive type generally are arranged in some fashion to respond to an impact of the vehicle with an obstruction or barrier thereby to deploy an air bag. It generally has been the practice to mount these devices on the vehicle in the region of and in association with the vehicle bumper or other front or rear end portion. Therefore, upon contact with an obstruction or barrier so as to deform or at least to yield in a crash environment a sensing mechanism in the device will respond to actuate means for inflation and consequent deployment of the air bag within the confines of the vehicle. The air bag so deployed then should be capable of carrying out its restraining function, i.e., to decelerate the forward momentum of the occupant following the collision. The ultimate aim is to prevent or at least reduce the chance of the occupant sustaining serious injury.
The prior art devices in large measure have not proved entirely satisfactory in operation. On particular problem with prior art devices is with regard to the speed of operation, i.e., the response time (T.sub.2 -T.sub.1) encompassing the interval between initial contact (T.sub.1) and terminating with an output (T.sub.2) resulting in inflation of the air bag. It should be appreciated that the deployment of the air bag should occur within an extremely short interval of time following a collision, otherwise there will be a diminution or loss of any safety factor since the occupant will have achieved a significant relative velocity with respect to the inside of the vehicle. The significance of a rapid response to the condition may be appreciated when it is considered, for example, that a bumper or other front or rear end portion of the vehicle hitting an obstruction or barrier at 55 mph is displaced approximately 3 inches in about 2.5 milliseconds time.
In addition, many of the prior art devices suffer from a problem characterized as a general inability to prevent deployment of the air bag upon impact of the vehicle with an obstruction or barrier when the vehicle is traveling at a low velocity. Normally, deployment of the air bag under this condition would not be required for safety purposes and, further, the deployment of the air bag at this time and under the circumstances possibly could result in injury to the occupant. Another aspect of this problem is the inadvertent deployment of the air bag in a "g"-type sensing device. In such a device, it is not uncommon to obtain a response to ordinary shock and vibration encountered in ordinary use of the vehicle. This aspect has its genesis in a difficulty in discriminating between a crash "signature" on the one hand and road shock, vibration, side impact or the equivalent on the other. Each vehicle has a slightly different "signature", the characteristics of which are dependent upon such factors and/or characteristics of shock absorbers, undercoating and frame rigidity, to name a few. And, as the vehicle ages, it is common that the factors and/or characteristics may change thereby changing this "signature". Thus, the device, first, must be tailored to the particular vehicle, and tailored again as, for example, aging sets in.
A further problem associated with certain of the prior art devices resides in a complication of constructions and lack of universality of their adaption to vehicles both of standard size and those of smaller and lighter size. Specifically, many of the known prior art devices for enabling inflation of an air bag within the confines of a vehicle are relatively large in size and weight. This is an important factor with many of the newer models.
One device which is representative of a segment of the prior art is described in U.S. Pat. No. 2,931,665 to Sander. Sander essentially describes the device as including an hydraulic system which actuates a switch during impact of the vehicle. Disadvantages associated with the Sander device are that it is extremely complicated in both construction and mode of operation, requiring several components and it must be especially adapted to various types of vehicles. A further disadvantage resides in the fact that a fluid pump must be operated in response to movement of the vehicle to properly enable actuation of the safety device. Accordingly, should the vehicle be stationary upon impact by a moving object, the air bag would not be deployed.
Another device representative of a further segment of the prior art is described in U.S. Pat. No. 3,072,760 to Hazen. This particular device is dependent upon acceleration of the vehicle for actuation of means for deployment of an air bag. A shortcoming of the Hazen device and others of similar nature is that its operation is dependent upon the physical crushing characteristics of the impacted object. Thus, the response time for the deployment of the air bag is determined, in part, by the particular physical properties of the obstruction. As a consequence, the device may not be actuated properly within the intended time interval should other than standard so-called barrier type objects be impacted.
Moreover, known devices of this type suffer from an additional problem in that their operation is dependent upon actual deformation of the vehicle during impact. And, if the device is to perform in the intended manner, it may, of necessity, require a specific construction for each model vehicle. Thus, this lack of universality renders them materially less versatile than might be otherwise possible.